The present invention relates to a process for the production of an implant as a bone substitute, in which use is made of a pattern of a material which is connectively open-celled throughout, the cells of which are filled with a core material of ceramic matrix composition, whereupon the material of the pattern is removed by firing the core material, the implant material being cast into the resultant cavities of the core and the core material finally being removed.
For producing a morphologically stable implant of metal or acid-proof plastics material as bone replacement having a connectively open cellular structure throughout, the procedure adopted according to a prior proposal consisted in that the interconnected cells of a sponge acting as an implant pattern, and consisting of a natural or plastics material, were filled with a ceramic matrix composition, the pattern material of which was removed from the core by application of heat whilst simultaneously solidifying the core. The implant material was then cast into the cavities remaining in the core and, after cooling or solidification respectively, the core material was dissolved by means of acids and removed by being blown out by sand-blasting to clean the core.
Conventional methods disclose the use of a plastic foam pattern material having connected pores which are limited by wall partitions or surfaces. If such pores are filled with liquid ceramic embedding mass, which is later burned into a rigid ceramic body, the following problem would result: parts of the burned-out foam pattern material remain adhered to the inner surfaces of the pores or cells and cannot be removed. The inventor has carried out many tests and experiments in an attempt to discover the source of this problem. He found out that adhering parts or residues of the burned-out foam pattern material disposed at the inner surfaces of the pores would eventually become attached to the metal of the bone implant to be produced. Such residues attached to the metal implant may cause later infections in the human body, as well as cancerous tumors and the like.
In attempting to resolve this problem, the inventor tried to make the limitations of the pores or cells of the foam pattern material as small as possible. He has found a plastic foam pattern material in which the limitations of the pores are very small, and the limitations consisting only of very fine or thin threads being reticulated to form a spatial grid or lattice network structure. Such thin threads naturally have to be reinforced by wax, for example, a water emulsion of wax can be applied on the threads at ambient temperature.
The use of water emulsion of wax as reinforcement coating on the threads substantially eliminates the aforementioned problem in the art. During the burning of the ceramic core, the water emulsion evaporates, producing a wrap or cover of evaporated water which escapes. Thereby the adhering of residues of foam pattern material to the inner surfaces of the ceramic core, and in turn to the metal implant, is substantially eliminated.
It was further discovered that the walls of the open-celled foam pattern material acting as a pattern, being expandable material in particular may be too thin under certain circumstances, so that the cavities remaining in the core after extraction of the pattern material may possible not be filled completely with the implant material of metal or plastics material, since its viscosity is too high with respect to the partially too small widths of the cavities.
It is an object of the invention to provide a process wherein the cavities remaining in the core material after removal of the pattern material from the core may be kept so large as to ensure the unobjectionable inflow of fluid metals or acid-proof plastics materials.